Photodynamic Therapy, PDT, is presently undergoing extensive clinical trials for the diagnosis and treatment of cancer. Regulatory approval of first generation PDT drug, Photofrin, was obtained in Canada in 1993, and regulatory approval in Japan and the Netherlands is expected in 1994. Filing of an NDA for Photofrin for use in esophageal cancer is scheduled for early 1994. Clinical trials of a number of second generation PDT drugs are in progress or are about to begin. These include SnET2, BPD, NPe6, mTHPC and ZnPc. For skin treatment, a laser source is not necessary, and adds a significant cost and complexity to the procedure. The availability of a low cost Light Emitting Diode (LED) light source for surface illumination of skin lesions would allow treatments to be done more cost effectively and allow the therapy to be done in a physician's office or small clinic. Additionally an LED array would be a more practical light source for large area applications such as advanced psoriasis. It is the objective of the this project to further develop and test an LED light source for photodynamic therapy, suitable for clinical use. The LED system will include all exposure control and dosimetry functions necessary to effect a PDT treatment, with controls designed for the clinician. The system will employ easily interchangeable LED treatment heads, available in several sizes, to allow the clinician to treat a selected area of affected skin. The system will be extensively tested in a mouse tumor model to quantify the response relative to laser sources. During the latter part of the first year and during the second year of the study, the system will be incorporated into the SnET2 Phase-II clinical trials for the treatment of cutaneous cancers.